Introductory statistics

Fractiles
Numbers that partition or divide an ordered data set into equal

Quartiles
Approximately divide a data set into 4 equal parts
There are 3

2nd Quartile, Q2
The Median of the entire data set
Half the data

1st Quartile, Q1
The Median of the Lower half of the data

3rd Quartile, Q3
The Median of the Upper half of the data

7 8 10 13 13 16 17 19 22 24 25

The Quartiles approximately divide the data into 4 equal parts, therefore

Example 1: the test scores of 15 employees enrolled in a

Example 2: The tuition costs (in thousands of dollars) for 11

Interquartile Range (IQR)
The difference between the third and first quartiles
IQR =

Find the Interquartile range from Example 1
Q1 = 10 and

Find the Interquartile range from Example 2
Q1 = 17 and

IQR – Interquartile Range (Q3 – Q1)
Gives an idea of

Take a look at Example 1 ? The IQR is 8

http://www.mathsisfun.com/data/images/box-whisker-plot.gif

Box and Whisker Plot
Example:

Box and Whisker Plot
A graph that shows the Median (Q2), Quartile

Steps for creating a box and whisker plot
Find the Median

Examples: Create a Box and Whisker Plot for each.
1. Years

2. 111 115 122 127 127 147
151 159 160 160 163 168

Distribution Shape Based on Box and Whisker Plot

If the median is